Part of the Plas Plant Colliery established in 1875 and closed in 1838 (NPRN 85027). The company was a pioneer in the use of electrcity underground, and the generating station at Plas Power was built to supply the company's other collieries at Gatewn and Fron as well as Plas Power itself. Such stations were eveolved from single power stations at each mine, but were quickly replaced as commercial power stations became more common.

The powerhouse is a tall building of a single storey with a semi-basement level. It is constructed of red brick with a slate roof and round-headed windows with brick voussoirs and stone cills, three to each of the east and west elevations. The north elevation has a central doorway flanked by an arched window to either side, and a large circular opening above the doorway which carried power cables. The south elevation originally had two similar arched windows, but these have been replaced with large double doors for vehicular access. Anothe blocked circular opening for cables is visible between them. There is a deeply corbelled cornice on all sides, together with a pronounced corbelled string course. there are many metal brackets on the exterior elevations which would have held insulators and cables.

The interior of the building is occupied by a steel frame, which is a later addition, cutting across the window openings. The floor is a shallow concrete slab.
(CADW listing description, building survey) S Fielding 25/04/05